Cathode-ray tube screen treatment



CATHODE-RAY TUBE SCREEN TREATMENT Filed June 19, 1951 FIG.1

ENERGIZATION AND VERTICAL SWEEP CIRCUITS HORIZONTAL SWEEP I2 L 1 J- -VERTICAL SWEEP OR POSITIONING CATHODE RAY TUBE IMPERFECTION 22 lo INDICATIONS SCREEN OSCILLOSCO PE 22 TO INTENSITY CONTROL CIRCUIT ADJUSTABLE AIR GAP 37 INVENTOR ARTHUR SAMUEL W y. ATTORNEY Patented May 20, i952 CATHODE-RAY TUBE SCREEN TREATMENT Arthur L. Samuel, Poughkeepsie, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application June 19, 1951, Serial No. 232,311

10 Claims.

development of storage systems in which the digits are represented by a charge pattern on the screen of a cathode ray tube. For this purpose conventional cathode ray tubes are employed in conjunction with a signal or pick-up plate,

consisting of a sheet of metal foil or gauze external to the tube and closely attached to the face thereof. Each elemental area of the screen is therefore capacity coupled into a common channel, as in the iconoscope.

A major drawback to the use-of this system, however, is that cathode ray tube screens produced even by the best manufacturing methods known in the past invariably have one or more imperfections which cause errors if the portion of the screen where the imperfection occurs is utilized for storage purposes. This has been recognized in the art, and various solutions have been suggested. Each of these solutions, however, has been in the nature of a compromise, such as utilizing a lower accelerating voltage for the tube than is otherwise deemed desirable or blanking electronically the imperfect portion of the screen utilized in the particular installation. The magnitude of the problem is apparent when it is realized that even with these compromising methods only from 10% to 50% of the cathode ray tubes commercially produced are usable for storage systems, and the remainder must be discarded either because of the number of imperfections on the screen of each tube on the large size of one or more of these imperfections on a particular tube.

The principal feature of this inventon is -the provisionof a process for the treatment of cathode ray tube screens which will remove these imperfections and produce uniformity of the screen.

The invention will be best understood from the following description and draw n s which disclose, by way of example, the princi le of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 shows diagrammatically a circuit arrangement for testing a cathode ray tube screen for imperfections; and

Fig. 2 shows a Tesla coil circuit of the type utilized in the treatment of cathode ray tube screens according to the invention.

As shown in Fig. 1, each cat ode ray tube IE3 is connected to an energization and vertical sweep circuit 1 2 whch energizes the tube electrodes and causes its electron beam to sweep its screen It in the vertical direction. A foil or conducting coatiing I6 is positioned on the face of the tube adlament the screen [4 as shown and is connected to the input of amplifier IS. The output of amplifier I8 is connected to the Z axis or intensity-control circuit of oscilloscope 20, whose horizontal sweep circuits are connected to the horizontal deflecting elements of tube 10 as indicated. The vertical sweep circuits of circuits 12 are also connected to the Y axis or vertical deflecting elements of oscilloscope 20, and thus the time base sweeps of tube Ill and oscilloscope 2B are in synchronism. The resultant scan on each is of the line-by-line type, but any desired form of scanning may be employed: 6. g., spiral,

1 interlaced, etc. In one embodiment, a 1 kc. horizontal sweep was employed with a 2 c. p. s. vertical sweep.

Alternatively, instead of providing a raster scanning the entire face of tube I0 in synchronism with the scanning of oscillo cope 20, a positioning voltage, manually controllable, might be applied to the Y axis input of oscilloscope 20 and to the vertical deflecting elements of tube It! instead of utiliz ng the vertical sweep circuit disclosed. Thus, merely a single line trace would appear on the face of tube [0 together witha corresponding single line trace on the indicator of oscilloscope 20, both traces being movable in synchronism up or down manually by adjustment of the positioning control.

At each portion of the screen l4 that the electron beam encounters an imperfection (or in other words, wherever the secondary emission ratio is more or less than that of the majority of the screen), the input to the amplifier 18 will be altered, resulting in an alteration of the intensity of the electron stream in the cathode ray tube of the oscilloscope 20. As a result, visible indications 22 of the imperfections of the secondary emissive surface or screen I4 of the cathode ray tube 10 will be determined. 1

These imperfections, which would render the tube unusable for storage purposes, as outlined above, may be removed in accordance with this invention by removing the foil ill from the. face of tube [0 and moving a probe connected to the high frequency hirh voltage output of Tesla coil over the face of the tube adjacentthe portions where the imperfections have beendetected, as described above. Usually only one .passage of the probe is requ-red over the tube face adjacent each imperfection. 'l' he electrostatic charge remaining on the tube It must, of course. thereafter be removed. Preferably foil 15 is then replaced and the entire screen M. of the cathode ray tube IE! reexamined by means of the circuit arrangement shown in Fig. 1 in order to determine that the imperfections have been removed and a uniform screen produced.

One convenient form of Tesla coil utilized has been the commercial Central Scientific Co. Catalogue No. 80730 High Frequency Coil of the Tesla Type. It is understood that the circuit of this is of the type shown in Fig. 2, which is given merely by way of example, andthat it produces:

an output of approximately 35 kv. The primary coil of transformer 30 is supplied with 110 v. 60 cycle A. C. and the turns ratioof this transformer is such that approximately 5,000 volts is proa duced across the secondary thereof. This high voltage is applied to a tank circuit 32. and ad-' justable air gap 35 in series. Tank circuit 32. includes an inductance 33 and a condenser 34 connected in parallel with their parameters chosen such that the' tank circuit 32 is resonant at approximately 500 kc. One terminal of the-second- .ary of transformer 30 is also grounded as shown.

The other terminal is connected through isolating condenser 36 to probe 31, which is applied to thefaceof the cathode ray tube H], as necessary, as'described above. The high alternating voltage applied across air gap 35 causes the air dielectric in the gap to break down, each time the sine wave exceeds a certain value as determined by the dimension of the gap. This breaking down of the air in the gap produces a ringing or oscillation of the tank circuit 32 at its resonant frequency, thereby producing bursts of high frequency energy'at probe 31 38' effectively isolates probe 31 from the A. C. power voltage but presents a negligible impedance to the high frequency energy.

While the process described above included only treatment of selected portions or areas of the cathoderay tube screen I4, i; e.', those which werei'ound to be imperfect as demonstrated by the: circuit arrangementinFig: 1, itis of course, apparent that the entire screen [4 may be so treated by'applying-probe' 31 to the face of tube I 0, either'elementalarea by'elemental area, or all at once by connecting foil ['6 to Probe 31 instead of to the inputlof amplifier I8.

The disclosed process for treatment of cathode ray tube screens has been demonstrated to be most effective, and it has been found that the .majority of the commercially available cathode ray tubes which were otherwise unfit for use in storage systemsof the type described above prior to treatment by this process had their imperfections removed and the screens rendered uniform after a single application of high frequency energy from a Tesla coil over the face of the tube.

While. there have been shown and described and'pointed outthe fundamental novel features of the invention, as applied to apreferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and" in its operation maybe made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicatedby the scope of the following claims.

What is claimed is:

l. The process of treating the screen of a cathode ray tube to remove imperfections and Isolating condenser 11 i produce uniformity thereof which comprises applying to the outer face of the tube a high voltage of alternating polarity.

2. The process of treating the screen of a cathode ray tube to remove imperfections and produce-uniformity thereof which comprises applying to the outer face of the tube a high frequency voltage:

3-. The process of treating the screen of a cathode ray tube to remove imperfections and produce uniformity thereof which comprises applying to successive elemental areas of the outer face of. the tube a high voltage of alternating polarity.

'4. The process of treating the screen of a cathode ray tube to remove imperfections and produceuniformity thereof which comprises applying to the-outer face-of thetubea high-voltage of high frequency.

5. Theprocess of treating the screen of a cathode ray tube to removeimperfections' and produce uniformity thereof which comprises applying to the outer faceof the tube an alternating' voltage of the order of several thousand volts.

6. The process of treating the screen of a cathode ray tube which comprises applying to the outer faceofthe tube a high frequency Tesla'coil output.

'7. The process of testing and treating the screen of a cathode ray tube which comprises scanning said screen elemental area by elemental area to determine imperfect; portionsthereof and thereafter applying an alternating voltage to the face of the tube adjacent the imperfect portions thus found to remove the imperfections.

8. The process of testing and treating the screen of acathode ray tube which comprises scanning said screen elemental area by elemental areato determine imperfect portions thereof and thereafter'applying' a high voltage ofalternating polaritytothe face of the tube adjacent the imperfect-portionsthus found to remove the imperfections.

9. The process of testing and treating the screen of a cathode rayt'ube" which comprises scanning said screen elemental area by elemental area to determine imperfect'portions'thereof and thereafter applying a high frequency voltage to the face of" the-tube adjacent theimperfect portions-thus found to-remove theimperfections.

10i The process of testing and treating the screen of a cathode ray tube which comprises scanning said screen elemental area by elemental area to determine imperfect portions thereof and thereafter applying ahigh' voltage of high frequency to the face of the tube adjacent the imperfect portions thus found to remove the imperfections.

ARTHUR L. SAMUEL.

REFERENCES CITED UNITED STATES PATENTS ,Name Date Denk' Nov. 8, 1949 Number 

